Pentaerythritoltetrakis-(3,5-di-t-butyl-4-hydroxy-benzylthioacetate)



United States Patent 0 U.S. Cl. 260-470 1 Claim ABSTRACT OF THEDISCLOSURE Organic materials can be stabilized with compounds having theformula "ice strength, and stability under load, that makes them usefulin the manufacture of pipe, film, wire, coatings, or various moldedobjects such as bottles and the like.

These polyolefins, however, are subject to considerable degradation atthe high temperatures that are required in their processing or that maybe encountered by the finished articles. They may also be degraded bychain cleavage resulting from oxidation or attack by acids. Themolecular breakdown which occurs in these polymers during fabrication isusually evidenced by increased brittleness at low temperature andreduced tensile strength and dielectric properties.

It is customary to incorporate small amounts of stabilizers into thepolymer to improve the resistance therewherein all of the ,ns are equalto each other and are within the range oil to 22.

This invention relates to compounds used as stabilizers for organicmaterials. More particularly, this invention is concerned with the useof these compounds as stabilizers and antioxidants for olefin polymersand to the polymer compositions stabilized therewith.

A rapidly expanding industry utilizing polyolefin resins has created aneed for stabilizers that will render the 60 wherein all of the ns areequal to each other and within finished articles of manufacture moreuseful, more versatile in application, and more nearly permanent.Polymers of aliphatic olefins have a combination of properties, such ashigh resistance to stress cracking, high tensile the range of 1 and 22.

A specific example of the stabilizers of this invention ispentaerythritoltetrakis-(3,5-di-t-butyl 4 hydroxybenzylthioacetate)having the formula Although this invention will be described with regardto the use of the novel compounds as stabilizers for polyolefins, it isunderstood that the compounds are suitable also as stabilizers for othermaterials, such as elastomers, including both natural and syntheticrubbers; synthetic resins, e.g., vinyl resins, polystyrene, polyamides,polyacetals, and polyesters; fats; gasolines; waxes; soaps; oils;grease; and so forth.

The materials with which this invention will be illustrated are thenormally solid homopolymers and copolymers of aliphatic olefins havingfrom 2 to 8 carbon atoms per molecule, such as ethylene, propylene,l-butene, isobutylene, Z-butene, l-pentene, and l-hexene, and mixturesthereof.

In general the amount of agent to be added to the polyolefin dependsupon the degree and kind of stabilization desired. The amount ofantioxidant can vary from about 0.001 to about 5.0 percent, based on theweight of the polyolefin, with amounts of approximately 0.05 to 0.5percent being preferred. As a rule, it is preferred to use the minimumamount required to achieve the desired results.

The compounds of this invention can be mixed with the polyolefin in anysuitable manner that will effect thorough distribution and dispersion.This can be accomplished in equipment suitable for mixing solids, as bymilling the polyolefin with the additive on heated rolls such as areused in the compounding of rubber or on other suitable milling or mixingequipment, such as for example Banbury mixer or conventional rubbermill. Instead of adding the stabilizing agent to the polymer in thesolid or molten state, it can be added to the solution or suspension ofpolymer in an organic solvent or to an aqueous dispersion thereof andthe volatile solvent subsequently removed by vaporization.

The antioxidants of this invention may be supplemented by small amountsof finely dispersed particles of carbon black to shield the polyolefinfrom the deleterious degradative effects of ultraviolet radiation,thereby improving its resistance to light deterioration. Carbon blackssuitable for use herein include both activated and unactivated types,such as channel carbon black, furnace carbon black, animal or vegetablecarbon black, thermal carbon black, light lamp blacks, acetylene blacks,and the like, and carbon blacks activated in the presence of suchmaterials as oxygen, sulfur, or selenium. The average particle size ofcarbon black used herein should be below about 1000 angstroms andpreferably below about 200 angstroms, so as to ensure a uniformdispersion of the carbon black through the polymer. Amounts of carbonblack within the range of about 0.05 to 5.0 percent by weight of thepolymer, and preferably about 0.1 to 3.0 percent, are satisfactory. Forsome polyethylene applications, carbon black concentrations of up toabout 50 percent by weight Melt index (M110) after can be present,especially where partially conductive polyethylene-carbon blackcompounds are employed.

The preparation of the novel stabilizers and their use in polyolefinresin compositions are illustrated by the examples which follow. It isto be understood, however, that these examples are given solely for thepurpose of illustration and that the invention is not to be regarded asbeing limited to any of the specific materials or conditions recitedtherein except as set forth in the appended claim.

EXAMPLE I Sodium (9.2 grams, 0.4 atom) was dissolved in 270 ml. ofethanol in a 500 ml. Ehrlenmeyer flask under a reflux condenser. Whenthe sodium was in solution, the flask was cooled to 10 C. and 43.2 gramsof pentaerythritoltetrakis (mercaptoacetate) (0.1 M) was added quickly.The solution of a sodium mercaptide was then emptied into a droppingfunnel.

Into a 3-necked, 2-liter Morton flask equipped with stirrer, N inlet,thermometer, reflux condenser, and dropping funnel was added 25.5 gramsof 3,5-di-t-butyl-4- hydroxybenzyl chloride (0.1 M), prepared by themethod disclosed by N. P. Neureiter in J. Org. Chem., 28, 3486- (1963),in ml. of ethanol. The flask was heated to 60 C., and the sodiummercaptide added dropwise but quickly to a pH of 7. Heating wascontinued for /2 hour at 60 C. The precipitated NaCl was removed byfiltering, and the filtrate evaporated to remove the ethanol. Theproduct,pentaerythritoltetrakis-(3,5-di-t-butyl-4-hydroxybenzylthioacetate), wasa thick viscous syrup.

Analysis.Calculated for C H O S (percent): C, 67.2; H, 8.3; S, 9.8.Found (percent): C, 67.09; H, 8.5; S, 9.68.

A satisfactory antioxidant should hold the chemical and physicalproperties of the original organic material during an acceleratedoxidation testing procedure, generally up to three hours duration. Forthe following examples, the test procedure consisted of milling onepound of polyethylene in air on a two-roll laboratory mill having afront roll speed of 25 r.p.m. and a back roll speed of 35 r.p.m. withthe distance between the two rolls adjusted to maintain a uniformrolling back in the nip and a mill temperature of 320 F. After thepolymer started to melt, 300 p.p.m. of the antioxidant was added.Samples (75 grams) were taken after 5, 30, 60, 90, 180 minutes, and meltindex, weight percent carbonyl, tensile elongation, and oxidationinduction time were determined. Oxidation induction time was determinedby Diflerential Thermal Analysis (DTA), indicating the degree ofoxidation resistance. The test involves oxidation of the polymer at 392F. and 100 percent oxygen. The analysis measures the length of timebefore oxidation starts. The melt index and elongation tests demonstratethe holding characteristics for the physical properties of the polymer;the carbonyl values, the holding of the chemical properties.

EXAMPLE II Percent C=O atter- Percent elongation 5 30 6O 90 180 30 90180 DTA, Sample min. min. min. mm. min. min. min. min. min. min. min.min. min. min A 5. 1 4. 4 4. 5 4. 8 08 013 015 019 027 050 146 149 6. 1B 2 1.6 2.8 4.3 4.7 5.1 .013 .14 .16 .23 .70 104 58 21 3 I A ispolyethylene+pentaerythritoltetrakis-(3,5-di-t-butyl 4hydroxybenzylthioacetate).

B is p y ene wit n t i i e References Cited UNITED STATES PATENTS11/1966 Dexter 25257 5/ 1966 Peterson 260-473 8/1964 Homberg 260-23LORRAINE A. WE-IN BERGER, Primary Examiner E. J. GLEIMAN, AssistantExaminer US. Cl. X.R.

